Chronic kidney disease is becoming more prevalent as the epidemic of type II diabetes spreads. Dialysis and transplantation can compensate for deteriorating kidney function, but each of these therapies has limitations: dialysis cannot replace all kidney functions, and the availability of matched organs for transplantation is restricted. Progress in regenerative medicine offers hope that individually matched kidney tissue may be generated de novo for afflicted patients. The adult kidney lacks the capacity for organogenesis, and therapies based on de novo nephrogenesis must recapitulate embryonic nephrogenesis. Our long term goal is to understand mechanisms by which renewal and differentiation of nephron progenitor cells is balanced by the immediate cellular environment or niche in the embryonic kidney, so that this process can be recreated in the adult. In the first project period we defined signaling pathways that control renewal of nephron progenitors, and in this application we propose to extend these studies to the important question of how niche signals control the balance between renewal and differentiation. Conceptual and technical advances made in the ongoing project allow us to approach this question from three complementary angles. The following aims are proposed: 1. Elucidate the mechanism by which BMP7 controls renewal of nephron progenitor cells through MAPK activation. 2. Define mechanisms by which the proteoglycan decorin controls nephron progenitor differentiation. 3. Model self renewal versus differentiation of progenitor cells in kidney organoids. Scientifically, we propose novel developments of the model for progenitor cell turnover in the nephron progenitor niche. In terms of technological innovation, we propose to develop a system for in vitro organogenesis from defined single cell suspensions of nephron progenitor cells in which the balance between renewal and differentiation can be studied. A potential medical innovation based directly on these studies would be the development of an organoid-based model of human genetic kidney disease such as polycystic kidney disease.